JP2005091198A - Welding fixture for measuring young's modulus in expansive concrete, and method for measuring young's modulus in the expansive concrete using the welding fixture - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a welding fixture for measuring the Young's modulus of expansion concrete that can measure the Young's modulus in the expansive concrete in a state in which a restriction is applied while the expansive concrete is being cured, and can measure the amount of distortion change after the restriction is released. <P>SOLUTION: The welding fixture is composed by fixing and mounting one end plate to one end side of a restriction steel material for applying a restriction to the expansive concrete while the expansive concrete is being cured, and by detachably mounting the other end plate to the other end side of the restriction steel material. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a restraining jig for measuring a Young's modulus when restraining the expanded concrete in the course of curing the expanded concrete, and a method for measuring the Young's modulus of the expanded concrete using the restraining jig.

  As is well known, the expansive material is used as a concrete admixture in order to compensate for shrinkage of cast-in-place concrete and concrete products in the field of civil engineering and construction, and to introduce chemical prestress, and exhibits a predetermined effect. Since the effect is widely recognized, in recent years, the amount of expansion material used is almost constant despite the fact that the amount of concrete produced in Japan has decreased.

  One application of such an expansion material is cast-in-place PC (precast concrete) slab. Currently, steel bridges with cast-in-place PC slabs currently under construction in Japan have a small number of main girders and longer spans for the purpose of rationalization and labor saving. The floor slab is thicker than RC (steel reinforced concrete) slabs. In addition, high-strength concrete using early-strength Portland cement is used, which may cause harmful temperature cracks due to the heat of hydration of the cement. For these reasons, expanded concrete is used as a cast-in-place PC floor.

  By the way, when such an expanded concrete is used for a cast-in-place PC floor slab, it is necessary to accurately estimate the temperature stress of the PC floor slab by FEM analysis (finite element method) or the like. It is necessary to accurately determine the Young's modulus of concrete.

  As described in Non-Patent Document 1 below, the Young's modulus of expanded concrete is obtained from the relationship between the stress and strain obtained from the load by applying a load to the cylindrical specimen and measuring the strain of the cylindrical specimen. ing.

  However, this method does not directly measure the Young's modulus of expanded concrete in a state where constraints are applied in the course of curing. As described above, the load is applied to the cylindrical specimen and the strain of the cylindrical specimen is reduced. It is only calculated indirectly from the relationship between the strain and the stress obtained from the load, and the Young's modulus of the expanded concrete is obtained indirectly. Therefore, there is room for examination as to whether the value is appropriate for the expanded concrete at the young age, particularly in the temperature stress analysis of the PC slab.

On the other hand, the strain changes after the restraint is released during the hardening of the expanded concrete, and the strain changes after the restraint is released. Anyway, it can be expected to contribute to the reduction of cracking of expanded concrete. Therefore, it is necessary to accurately measure the amount of strain change after the constraint is released in order to plan countermeasures for temperature cracks.
Japanese Industrial Standards: Static modulus test of concrete (JIS A 1149: 2001)

  The present invention has been made in view of the above points, and can measure the Young's modulus of expanded concrete in a state in which a constraint is applied during curing, and measure the amount of strain change after the constraint is released. An object of the present invention is to provide a restraining jig for measuring Young's modulus of expanded concrete.

  In order to solve such problems, the present invention was made as a restraining jig for measuring Young's modulus of expanded concrete and a method for measuring the Young's modulus of expanded concrete using the restraining jig. One of the features of the restraint jig for measuring Young's modulus is that one end plate is fixedly attached to one end side of a restraining steel material for restraining the expanded concrete in the course of hardening of the expanded concrete, The other end plate is detachably attached to the other end side.

The characteristic of the method for measuring the Young's modulus of expanded concrete is that the expanded concrete is filled into the filling portion 4 surrounded by the restraining steel material 1 and the both end plates 2 and 3 of the restraining jig as described above. The other end plate 3 detachably attached to the other end side of the restraint steel material 1 is removed from the restraint steel material 1 and the strain change amount (ε1) of the restraint steel material 1 when restraint is released and the filling portion 4 is filled. The strain change amount (ε2) of the expanded concrete was measured, and the measured strain change amount (ε1) of the constrained steel material and the strain change amount (ε2) of the expanded concrete were substituted into the following formula (1). The Young's modulus (Ee) of the expanded concrete is calculated and the Young's modulus (Ee) of the expanded concrete is measured.
(In formula (1), Ac is the cross-sectional area of the concrete, As is the cross-sectional area of the restraining steel, and Es is the Young's modulus of the restraining steel)

  In this case, it is also possible to measure the Young's modulus of the expanded concrete by changing the diameter of the constrained steel material 1 in order to increase the strain amount when the constraint is released and to increase the measurement accuracy of the Young's modulus of the expanded concrete. In general, the diameter of the constraining steel material is 11 mm as a standard, but the diameter of the constraining steel material 1 can be changed to, for example, 9.2 mm or 13 mm.

The restraint jig of the present invention has the above-described configuration, and the restraint jig is used to measure the strain change amount of the restraint steel material and the strain change amount of the expanded concrete as described above, and the restraint steel material thus measured is measured. Since the Young's modulus of expanded concrete is calculated from the amount of strain change and the amount of strain change of expanded concrete, it is not indirect as in the conventional method of loading a specimen, but restrained during curing. There is an effect that the Young's modulus of the expanded concrete to which is added can be directly measured.
In addition, there is an effect that it is possible to measure the amount of change in the concrete strain after releasing the constraint on the specimen in which the Young's modulus at the time of releasing the constraint is measured.

  As shown in FIG. 1, the restraining jig 5 of one embodiment has one end plate 2 fixedly attached to one end side of the restraining steel material 1 and the other end on the other end side of the restraining steel material 1. The plate 3 is configured to be detachably attached.

More specifically, one end of the restraining steel material 1 is fixed to one end plate 2 having a thickness of 30 mm by welding and the other end is fixed to the other end plate 3 having a thickness of 30 mm by screwing. The restraint steel material 1 and the end plate 3 can be removed depending on the age. A space portion surrounded by the restraining steel material 1 and the both end plates 2 and 3 is formed as a concrete filling portion 4.

  Next, an embodiment of a method for measuring the Young's modulus of the expanded concrete and the amount of strain change after releasing the constraint using the constraint jig 5 having the above-described configuration will be described.

  First, a strain gauge (not shown) is attached to the center of the restraining steel material 1 in advance, and a vinyl tape (not shown) is attached to the restraining steel material 1 in order to remove adhesion between the restraining steel material 1 and the concrete when the restraint is released. Wrap it in layers, and then wrap a sheet of fluororesin (not shown) 0.5 mm thick in quadruples.

  Next, as shown in FIG. 2, the restraining jig 5 is placed in a rectangular mold 6 surrounding the four sides. In this case, a polyester sheet (not shown) is previously installed in the mold 6 in order to cover the specimen after removing the mold 6 and prevent moisture from escaping. In addition, grease is applied in advance to the inner sides of both end plates 2 and 3 so that the restraining jig 5 can be easily removed except for adhesion to concrete when the restraint is released.

  Next, as shown in FIG. 3, the expanded concrete is driven into the mold 6 in which the restraining jig 5 is installed as described above. As a result, the expanded concrete is filled in the filling portion 4 surrounded by the restraining steel material 1 and the both end plates 2 and 3 in the mold 6. Then, the driving surface (the upper surface surrounded by the mold 6) is temporarily covered with a vinyl sheet to protect it.

  And surface finishing is performed 1 to 2 hours after the settlement of concrete settles, and then the driving surface is completely covered with a polyester sheet to form a sealed state.

  Next, the strain gauge cable affixed to the restraining steel material is connected to the data logger and measurement is started. In this case, in order to remove the restraint of the formwork as much as possible, loosen the bolts fixing the uniaxial restraint specimen (hardened expansive concrete hardened) and the formwork measurement surface at the initial setting time, and leave it as it is. The mold 6 is removed at the first test material age (the age at which the constraint is released and the Young's modulus of the expanded concrete is measured).

  Then, from 3 hours before the predetermined test material age, a part of the polyester sheet covering the four sides of the specimen is cut out, and a strain gauge is attached to the specimen (concrete).

  In this state, as shown in FIG. 4, the other end plate 3 on the removal side is withdrawn, and the strain change amount (ε1) of the restraint steel material 1 and the strain change amount (ε2) of the concrete at the time of restraint release are measured.

  The strain change amount (ε1) of the constrained steel material and the strain change amount (ε2) of the concrete are substituted into the following equation, and the Young's modulus (Ee) of the concrete when the constraint is released is calculated from the following equation. Here, in the following formula, (Ac) is the cross-sectional area of the concrete, (As) is the cross-sectional area of the restraining steel material, and (Es) is the Young's modulus of the restraining steel material.

  Next, the end plate 2 and the restraining steel material 1 on the fixed side are extracted from the specimen. And the specimen which removed the restraint jig 5 which consists of the end plate 2 and the restraint steel material 1 is made into a sealing state again, a concrete strain is measured with the strain gauge stuck on four side surfaces of the specimen, and the strain change after restraint release. Measure the amount.

  As described above, the constraint jig 5 directly measures the Young's modulus of the concrete and the amount of strain change of the concrete after the constraint is released.

  Examples of the present invention will be described below.

  By using the above-mentioned restraining jig, the above-described method was used to test the change over time in the Young's modulus of the expanded concrete, and the change over time in the strain change amount of the concrete after the release of the restraint was tested. Two types of concrete were tested: those containing early strong cement and those containing low heat cement.

  The test material age is 0.75 days, 1 day, 1.5 days, 2 days, and 3 days when concrete containing early-strength cement is used, taking into account the strength development properties depending on the type of cement, including low heat cement In the case of using concrete, it was set as 2, 3, 4, and 7 days.

  Three specimens of one material age are used, two of which are subjected to compression loading one hour after releasing the restraint at the test material age, and the other one is subjected to creep recovery strain and re-expansion strain using a strain gauge for one week. The measurement was continued. The test for one formulation was performed at least twice to minimize the effect of strain measurement error on Young's modulus.

  FIG. 5 shows the change over time of the Young's modulus of the expanded concrete containing the early strong cement measured using the restraining jig, and FIG. 6 shows the change over time of the Young's modulus of the expanded concrete containing the low heat cement. For comparison, a method of measuring a load by loading it on a conventional cylindrical specimen was also tested.

As is clear from FIG. 5, in the case of expanded concrete containing early-strength cement, the Young's modulus in the conventional measurement method was higher until the age of 2 days. The Young's modulus in the measuring method using tools was higher.
Although the reason why such a phenomenon occurs is not clear, it is estimated as follows. At the time of expansion, not only the restraining steel material but also the aggregate restrains the expansion of the cement matrix, so that tensile force acts on the aggregate as a reaction force. At the time of releasing the restraint, the restraint of the restraint steel material is almost completely released, but the restraint by the aggregate is not completely released and remains to some extent and satisfies the balance of internal forces. At that time, it is said that many elements that cannot bear an external force due to variations in expansion strain exist at the interface between the aggregate and the cement matrix, so-called transition zone. Therefore, since the tensile force remains in the aggregate as a reaction force that restrains the cement matrix even when the restraint is released, the Poisson effect due to the above-described tensile force between elements that cannot bear some external force present at the aggregate interface The transmission of force due to contact between elements is hindered. On the other hand, when a cylindrical specimen is loaded in the comparative example (conventional method), a compressive force acts on the aggregate, and due to its Poisson effect, between the elements that cannot bear some external force existing at the aggregate interface. The force is transmitted by contact, and the Young's modulus increases because the external force is borne by more elements. That is, it is estimated that the Young's modulus at the time of restraint release is smaller than the Young's modulus at the time of loading because the Young's modulus at the time of loading is more strongly affected by the element that resists a part of the external force caused by the variation in expansion strain in the cement matrix.
On the other hand, when the age of the material has passed for a certain period of time, as the hydration progresses, the defects caused by the variation in expansion strain are filled, or the hydration product compensates, so that the generation of micro components with small variations in the initial strain is generated. Come out. Therefore, it is estimated that the Young's modulus at the time of releasing the restraint using the restraining jig is almost equal to the Young's modulus at the time of loading in the comparative example. The age of this equivalent time is recognized to be about 2.5 days in the test results of FIG. 5, and when this age is exceeded, the Young's modulus using a restraining jig increases rapidly.

  Further, as is clear from FIG. 6, in the case of expanded concrete containing low heat cement, the Young's modulus in the conventional measurement method was higher until the age of 4 days. The Young's modulus in the measurement method using a jig was higher. The reason why such a phenomenon occurs can also be explained for the same reason as in the case of the test result of FIG. 5 described above. However, in the case of expanded concrete containing low heat cement, the progress of hydration is slow, so a restraining jig is used. The age at which the measured Young's modulus is higher than the Young's modulus by the conventional measuring method is as late as 7 days.

  Further, FIG. 7 shows the change over time in the strain change after the restraint release of the expanded concrete containing the early strong cement using the restraining jig, and the change over time in the strain change after the release of the restraint of the expanded concrete containing the low heat cement. Is shown in FIG.

  As is clear from FIG. 7, in the case of expanded concrete containing early-strength cement, the change with time in the amount of strain change after release of restraint did not change much with the age of the material after release of restraint.

  On the other hand, in the case of the expanded concrete containing the low heat cement, as is clear from FIG. 8, the change over time in the amount of change in strain after the release of the constraint was significantly different depending on the age of the material after the release of the constraint. Specifically, the shorter the age days after the restraint release, the greater the amount of strain change after the restraint release. However, the change over time was not so observed for any age.

  The expanded concrete used in the test contains cement, expanded material, fine aggregate, coarse aggregate, and admixture, and the types and physical properties thereof are as shown in Tables 1 to 4.

  Moreover, the compounding quantity of each material component is as Table 5.

  The present invention is a restraining jig for measuring the Young's modulus of expansive concrete, in which cast-in-place concrete in the field of civil engineering and construction, and expansive material used for shrinkage compensation of concrete products and introduction of chemical presses are mixed. It can be widely used for measuring Young's modulus of expanded concrete.

Sectional drawing of the restraining jig | tool of one Embodiment. The top view of the state which installed the restraining jig in the formwork. Sectional drawing of the state in which concrete is driven. Sectional drawing of the state which removed the other end plate. The graph which shows the time-dependent change of the Young's modulus of the expansion concrete containing an early strong cement. The graph which shows the time-dependent change of the Young's modulus of the expansion concrete containing a low heat cement. The graph which shows the time-dependent change of the strain variation | change_quantity after restraint release | extrication of the expansive concrete containing an early strong cement. The graph which shows the time-dependent change of the strain variation | change_quantity after restraint release of the expansion concrete containing a low heat cement.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Restraint steel material 2 ... End plate 3 ... End plate 4 ... Filling part

Claims (3)

  One end plate (2) is fixedly attached to one end side of the restraining steel material (1) for restraining the expanded concrete in the course of hardening of the expanded concrete, and the other end side of the restraining steel material is the other end side. A restraint jig for measuring Young's modulus of expanded concrete, wherein the end plate (3) is detachably attached. The expansion concrete is filled in the filling portion (4) surrounded by the restraining steel material (1) of the restraining jig according to claim 1 and both end plates (2), (3), and then the restraining steel material (1) The other end plate (3) removably attached to the other end side is detached from the restraining steel material (1), and the strain change amount (ε1) of the restraining steel material (1) at the time of restraint release and the filling portion (4) The strain change amount (ε2) of the expanded concrete filled in the inside is measured, and the strain change amount (ε1) of the constrained steel material (1) and the strain change amount (ε2) of the expanded concrete are expressed by the following formula (1). A method for measuring the Young's modulus of expanded concrete, wherein the Young's modulus (Ee) of the expanded concrete is measured by substituting and calculating the Young's modulus (Ee) of the expanded concrete when the constraint is released.
(In formula (1), Ac is the cross-sectional area of the concrete, As is the cross-sectional area of the restraining steel, and Es is the Young's modulus of the restraining steel)   The Young's modulus of the expanded concrete is measured by changing the diameter of the constrained steel material (1) in order to increase the strain amount when the constraint is released and to increase the measurement accuracy of the Young's modulus of the expanded concrete. Item 3. A method for measuring Young's modulus of expanded concrete according to Item 2.